Now that I got your attention, I'll have to explain. While looking for something else, I found a lot of "affordable" 50mm f/0.95 lenses on ebay. After the wow factor wore off it was time to figure out the practicalities.

Firstly they're C-mount or similar. As far as I understand this is used in security cameras and such like. The register distance (distance from mount to focal plane) is 17.5mm. Problem 1: most DSLRs are around 40mm or higher. Problem 2: the intended image circle are typically smaller even than APS-C so it will probably vignette.

There's no getting around problem 2, so the question remains what would it be like to fit to a DSLR? Assuming you had a mount adapter, it would fit as if you put an extension tube on for macro work. You will lose infinity focus and be limited to close up work.

One final thought appeared though - micro four thirds format. With the mirror binned, that has a register distance of 20mm so it is really close. With a little physical hacking of the lens body that might even fit.

Todo: work out how extension tubes affect focal distance.

Anyway, they're not quite cheap enough for me to experiment with in this respect, but if you want a really fast lens for macro use this might be something more exotic to play with.

We've just had a thread on a similarly specified lens over in the Canon section which you can read here. Are the lenses you are talking about definitely C mount or are they actually the Canon S mount lenses fitted with an adaptor?

Im not sure if this will work, but the way i see it, theres only one thing to do:
get some kind of adapter that works (canon to c or whatever mounts), and if this does not excist, you have to make one yourself. once you get a hold of one of these, you have to split it in two, and mount a tube (material not important, but inside must be non reflective) with the lenght equivalent of the difference between the two register distances (40mm - 17.5mm) and simply glue both halfs on each end of the tube, then it should be fixed?

but really, i dont know about how to fokus and so on, i just came to think of it